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And it's taken as a long time to realize how important that can be but when that happens then the whole system plays itself out, just as I showed you a moment ago
人们花了很久才意识到这非常重要，这之后，整个系统就能运作了，如我刚才讲的那样
So whether you get it from 1,25D coming in from the outside 1,25D, or 25D you make it inside the cell, the same thing happens
不管是从外界来还是25D在细胞内生成，后面都一样
but we now understand that this is the way the tissues are designed to work
现在我们知道这是组织工作的方式
It's the 25D present in the serum which gets into the tissues and then is converted to 1,25D
血清内有25D进入组织然后转化为1,25D
And the reason for that if you stop to think about it is that 25D is present in the serum and that's thousand fold greater concentration than is 1,25D
你们可以想想原因，25D存在于血清中浓度是1,25D的一千倍
So there's three orders of magnitude more molecules of 25D present in the tissues than there is 1,25D and that becomes important
组织中25D的分子数大出三个数量级，这非常重要
because each tissue can make the amount of 1,25D it needs independent of what the other tissues have or need
这让每个组织都能制造足够的1,25D而不用管其它组织的情况
It can do it when it needs it and is not dependent upon a "one-size fits all" circulating through the body stream basing all the tissues at the same time
需要就能制造，不需要所有组织都依赖于一刀切的系统循环
It wouldn't want to activate all of those systems at the same time. That wouldn't make any sense
不需要同时激活所有这些系统，这没有任何必要
I mean, if you're the good lord in designing the system you would do it this way rather than working through a circulating 1,25D level
我是说，如果你是造物主，你也会这样设计，你也不会通过1,25D循环来进行
The only tissue that really respond importantly to circulating 1,25D is intestine mucosa and that's in the control of calcium absorption
唯一依赖1,25D循环的组织是肠粘膜控制钙吸收
